The present invention relates to solid-state imaging apparatus for use for example in a video camera or digital still camera, and more particularly relates to the solid-state imaging apparatus using amplified solid-state imaging device which has an amplification function within its imaging region.
In recent years, CMOS (Complementary Metal Oxide Semiconductor) type image sensors are drawing attention and are practically used as solid-state imaging device. MOS type image sensors, as compared to CCD (Charge Coupled Device) type image sensor, is capable of being driven by a single power supply, and MOS image sensors can be manufactured through an identical manufacturing process as other LSI's while CCD image sensors do require an exclusive manufacturing process. For this reason, the MOS image sensor can be readily formed into an SOC (System On Chip) so as to be imparted with a multiple of functions. Also, since the MOS image sensor has an amplification circuit in each pixel so as to amplify signal electric charge within pixel, it is less likely to be affected by noise that occurs due to transmission path of signal. Further, the MOS image sensor is capable of selectively extracting signal electric charge of each pixel, and in theory of arbitrarily controlling pixel by pixel an accumulation time of signal and/or the order according to which it is read out.
Now, with the MOS image sensor, when a high-luminance light is incident, a change in potential occurs toward right and left of a region on which the high-luminance light is incident so that an image is obtained as if a white band-like light is incident. Such a phenomenon in the present specification will be referred to hereinafter as “transverse stripe phenomenon at the time of incidence of high-luminance light”. FIG. 1 schematically illustrates an image when the transverse stripe phenomenon at the time of incidence of high-luminance light occurs. Shown in FIG. 1 is a case where a high-luminance light is incident in the vicinity of a center whereby a band-like transverse stripe due to change in potential is seen in the direction of its left and right. The transverse stripe phenomenon at the time of incidence of high-luminance light will be described below together with an operation of typical MOS image sensor.
FIG. 2 shows a block diagram of a typical MOS image sensor. For ease of explanation, the MOS image sensor 2 shown in FIG. 2 has a pixel section structure where pixels are arranged into 4 rows by 4 columns. Its construction is as follows. In particular, the MOS image sensor includes: constant current supplies 2-5 connected to a ground line 2-4; pixels 2-6 for converting light into electrical signals; and CDS circuits 2-8 connected through vertical signal lines 2-7 for removing noise components of pixels. The CDS circuits 2-8 are respectively connected to column select switches 2-9, and the column select switches 2-9 are further connected to an output amplifier 2-11 through a horizontal signal line 2-10. The pixels 2-6 are controlled by pixel reset pulse φRS, electric charge transfer pulse φTX, and pixel select pulse φSE that are generated from a vertical scanning circuit 2-1 upon receiving of signal from a control signal generation circuit 2-3; the column select switches 2-9 are controlled by column select pulse φH that is generated from a horizontal scanning circuit 2-2 similarly upon receiving of signal from the control signal generation circuit 2-3; and the CDS circuits 2-8 are controlled by clamp pulse φCL and sample-and-hold pulse φSH that are similarly generated from the control signal generation circuit 2-3.
FIG. 3 shows a circuit construction of the MOS image sensor 2 with taking notice of certain one column in FIG. 2.
Like components as in FIG. 2 are denoted by like symbols as in FIG. 2. The constant current supply 2-5 includes a constant current supply transistor M1 connected to a constant current supply gate line 3-1. The pixel 2-6 is to convert an irradiated light into an electrical signal and output it to the vertical signal line 2-7. The pixel 2-6 includes: a pixel reset transistor M2; a charge transfer transistor M3; an amplification transistor M4; a pixel select transistor M5; a photodiode PD; and a floating diffusion section FD. The transistors within the pixel 2-6 are respectively connected to a pixel power supply line 3-2 that is shared by all the pixels, and to a pixel reset pulse line 3-3, a charge transfer pulse line 3-4, and a pixel select pulse line 3-5 that are shared by the pixels arranged in row direction.
The CDS circuit 2-8 is to remove noise components that are different from one pixel to another, and includes: a clamp capacitor C1; a clamp transistor M6; a sample-and-hold capacitor C2; and a sample-and-hold transistor M7. The transistors within the CDS circuit 2-8 are respectively connected to a clamp voltage line 3-6, a clamp pulse line 3-7, and a sample-and-hold pulse line 3-8. The column select switch 2-9 includes a column select transistor M8 that is connected to a column select pulse line 3-9.
FIG. 4 explains an operation in the case where high-luminance light is incident on a certain one pixel in thus constructed MOS image sensor so that the transverse stripe phenomenon at the time of incidence of high-luminance light occurs. FIG. 4 represents a portion of the MOS image sensor 2 shown in FIG. 2, where like components as in FIG. 2 are denoted by like reference symbols. For ease of explanation, the pixels in FIG. 4 are arranged in a two-dimensional lattice of 3 rows by 3 columns, where a pixel on the second row in the first column for example is denoted by 2-6(21). Further, a constant current supply for the first column for example is referred to as the constant current supply 2-5(*1).
A description will be given below of an operation mode of the pixel 2-6(23) on the second row in the third column when a high-luminance light is incident on the pixel 2-6(21) on the second row in the first column.
(1) As the high-luminance light is incident on the pixel 2-6(21) on the second row in the first column, the potential on the first column vertical signal line 2-7(*1) connected to the pixel 2-6(21) falls.
(2) The first column constant current supply 2-5(*1) operates in non-saturation region.
(3) A current value on the ground line 2-4 is lowered so that a voltage drop at a wiring resistance R1(*3) becomes smaller.
(4) A gate-source voltage of the constant current supply transistor within the third column constant current supply 2-5(*3) is increased so that an electric current greater than normal flows into the third column vertical signal line 2-7(*3). As a result, the gate-source voltage of the amplification transistor within the pixel 2-6(23) on the second row in the third column is also increased so that a voltage lower than normal is outputted, i.e. brighter as an image. A similar phenomenon occurs of all the pixels in the row direction.
To deal with such transverse stripe phenomenon at the time of incidence of high-luminance light, methods as in the following have been proposed for example in Japanese Patent Application Laid-Open 2001-230974. Particularly in the proposal, a circuit for clipping a voltage on the vertical signal line for example is separately provided whereby the voltage on the vertical signal line is controlled so as not to OFF the transistor within the constant current supply in periods for reading a signal of an incident light.
By clipping the vertical signal line with providing a clip circuit on the vertical signal line so as not to cause to OFF the transistor within the constant current supply as in the above prior-art proposal, the transverse stripe phenomenon at the time of incidence of high-luminance light can be reduced.